Conventionally, a wireless communication system includes an in-vehicle apparatus equipped to a vehicle and a mobile device carried by a user, and the in-vehicle apparatus and the mobile device perform duplex communication with each other. As an example of the wireless communication system, a smart system is widely known. In this smart system, a vehicle-side request signal is transmitted from the in-vehicle apparatus to the mobile device using an LF band so that the vicinity of the vehicle is a communication area and a mobile-side signal is replied from the mobile device to the in-vehicle apparatus in response to the vehicle-side request signal, and the in-vehicle apparatus actuates an actuator (door unlocking device, door locking device, lamp device, or the like) in the vehicle.
With respect to above-described smart system technology, there is a demand for broadening an attainable range of the vehicle-side request signal. One of methods for broadening the attainable range of the request signal is to extend an LF output of the in-vehicle apparatus. However, a strength of the request signal to be transmitted increases with an extension of the LF output. Therefore, when there is a limit to an increase of the field strength of the request signal (for example, when intensities higher than a certain upper limit are prohibited by the Radio Law), the method of extending the LF output cannot be applied in order to broaden the attainable range of the vehicle-side request signal.
If the attainable range of the vehicle-side request signal is broadened, the area within which the mobile device is positioned is extended, and the position of the mobile device cannot be accurately specified. This may prevent the enhancement of marketability.
That is, for the enhancement of marketability, it is required not only to broaden the attainable range of the vehicle-side request signal but also to enable the more accurate specification of the area where the mobile device is positioned.